Research On The Technology Of Logging Signal Enhancement Based On Maximum Ratio Combination

With the in-depth development of oil and gas production, it’s obvious that wireless transmission of downhole parameter plays an important role in evaluating the reservoir scale and exploitation value. Whereas for the increasing depth and complex construction environment, signal received by the Ground Receiving System can be terrible weak. At this point, how can we interpret the weak logging signal accurately becomes a difficult problem to be solved.Based on the wireless transmission of downhole data, and the basic principle of Diversity Combining, we combine the logging signals received by multi-antenna with some consolidation strategies and enhanced output signal can be obtained. Traditional signal merging schemes, such as Maximum Ratio Combining(MRC) and Equal Gain Combining(EGC), only consider the situation that no correlation exists between branches. However, in the application of Well Logging, the signals received by multi-antennas are not independent of each other. As a result of fact, the traditional MRC algorithm may not be suitable in that application.In the thesis, we proposed an optical merging scheme taking the correlation of branches into consideration, based on the analysis of traditional Diversity Combining technology. And we derived the expression of the combining weights for each branch under AWGN channel. Furthermore, for the application of Logging, we proposed a Data-Aided SNR estimation algorithm based on training sequence, which does well in weak signal estimation.Finally, a set of experiments were taken to conduct a performance analysis of the new merging scheme, including the optical combination of multi branch signals with Binary Phase Shift Keying(BPSK) modulation under fading channel, the output SNR and bit error rate analysis and performance comparison of the scheme for real logging signal. Experimental results show that, the proposed scheme can improve the output SNR of the received signal, thus reducing the bit error rate effectively, comparing with the traditional combining technology.